You may find that you never use the RPP system directly -- the lim interface is more attractive and has a much lower learning curve -- so it will only be discussed briefly. The RPP system is a collection of programs that operate on packages, with which you can install, uninstall, track and verify individual source and binary packages. The four most often used are rpp-install, rpp-uninstall, rpp-query and rpp-verify. rpp-build is used to actually create RPP packages.
Should you venture outside the lim into the underlying RPP system, please read the man pages for the rpp programs and rpp(5) for all the gory details.